In a communication system, it is desirable to have a path for transmitting a signal and a path for receiving a signal separated from each other, so as to avoid or reduce interference between the transmission signal and the reception signal which may degrade the quality of communication.
On the other hand, when a communication system uses two or more antennae simultaneously, for example, when a communication system has two respective antennae for two different communication schemes, e.g., SVLTE (Simultaneous Voice and LIE), SVDO (Simultaneous Voice and EVDO), a signal transmitted via one antenna often may be received at another antenna and added to a reception signal of the other antenna, thereby degrading the quality of communication. An example of such interference is third-order intermodulation (IMD3) distortion.
Conventionally, an isolator and/or a ceramic notch filter (i.e., band stop filter), which can remove an interference in a certain frequency band, have been employed so as to reduce the interference between the transmission signal and the reception signal and/or the interference between different communication schemes. However, use of an isolator and/or a ceramic notch filter may result in an increase in the physical size and cost of the communication system, while failing to sufficiently reduce interference.